Anesthetic vaporizer

ABSTRACT

An anesthetic vaporizer is disclosed having a linear flow system which insures precise predictability of the desired anesthetic composition. The total flow into the vaporizer is divided into two main gas streams, the first gas stream proceeds through precise linear flow restrictors and is then subdivided into two gas substreams by a concentration valve. One of the substreams is directed by the concentration valve through a vaporizing chamber where it becomes saturated with anesthetic and then to the vaporizer outlet. The other substream is channeled past the concentration valve directly to the vaporizer outlet where it is reunited with the one substream. By adjusting the concentration valve, the ratio of the substreams may be changed, thus affecting the eventual concentration of the anesthetic composition from the vaporizer outlet. The second main gas stream proceeds through a thermal compensation valve and is subdivided into two substreams, one of which is directed through fixed linear flow restrictors to the vaporizer outlet, and the other substream is directed through a variable thermal bypass also having linear flow restrictors. The flow through the variable thermal bypass to the vaporizer outlet is varied in accordance with the sensed temperature in the anesthetic vaporizing chamber. A feature of the vaporizer is the use of unique precise linear flow restrictors in every path of flow through the vaporizer so that a predictable anesthetic concentration is obtained and overall linear response is achieved despite variables occuring during operation of the vaporizer.

United States Patent [191 Sielaff [451 Oct. 15, 1974 ANESTHETICVAPORIZER [75] Inventor: Ulrich Sielaff, McFarland, Wis.

[73] Assignee: Airco, Inc., New York, N.Y.

[22] Filed: July 16, 1973 [21] Appl. No.: 379,506

[52] US. Cl. 239/136 [51] Int. Cl B05h 1/24, B44d 3/42 [58] Field ofSearch 239/135, 136, 137, 138

[56] References Cited UNITED STATES PATENTS 2,886,689 5/1959 Garth239/138 3,559,886 10/1968 Howard 239/136 Primary Examiner--Lloyd L. KingAttorney, Agent, or FirmRoger M. Rathbun; Edmund W. Bopp; H. HumeMathews [5 7] ABSTRACT An anesthetic vaporizer is disclosed having alinear flow system which insures precise predictability of the desiredanesthetic composition. The total flow into the vaporizer is dividedinto two main gas streams, the first gas stream proceeds through preciselinear flow restrictors and is then'subdivided into two gas substreamsby a concentration valve. One of the substreams is directed by theconcentration valve through a vaporizing chamber where it becomessaturated with anesthetic and then to the vaporizer outlet. The othersubstream is channeled past the concentration valve directly to thevaporizer outlet where it is reunited with the one substream. Byadjusting the concentration valve, the ratio of the substreams may bechanged, thus affecting the eventual concentration of the anestheticcomposition from the vaporizer outlet. The second main gas streamproceeds through a thermal compensation valve and is subdivided into twosubstreams, one of which is directed through fixed linear flowrestrictors to the vaporizer outlet, and the other substream is directedthrough a variable thermal bypass also having linear flow restrictors.The flow through the variable thermal bypass to the vaporizer outlet isvaried in accordance with the sensed temperature in the anestheticvaporizing chamber.

A feature of the vaporizer is the use of unique precise linear flowrestrictors in every path of flow through the vaporizer so that apredictable anesthetic concentration is obtained and overall linearresponse is achieved despite variables occuring during operation of thevaporizer.

8 Claims, 9 Drawing Figures PAIENIED w I 5 9 mm 10? a Pmmsuwww 3.841560MEF 20? Q WWW 1X t ANESTHETIC VAPOZER tus, and more specifically relatesto anesthetic vaporizing apparatus of the type which is provided with avaporizing chamber and a bypass channel connected in parallel therewith.

Numerous varieties of anesthetic vaporizing apparatus are known whichare so constructed that gas flow through the apparatus is divided with afirst portion proceeding through the vaporizing chamber thereof, and asecond portion proceeding through a bypass channel connected in parallelwith the vaporizing chamber. Operation of devices of this type rely uponproducing saturation of the gas passing through the vaporizing chamber;it is then only necessary to properly proportion the amount of gaspassing through the vaporizing chamber to the total amount of gasthrough the vaporizer to be able to predict the concentration of vaporin the resulting mixture. While in principle, therefore, it would seemthat achievement of a desired concentration of vapor in the mixtureprovided by such apparatus should be readily achieved, it isnevertheless found in practice that the concentration of vapor ismaintained at a desired level only with the greatest difficulty.Problems with apparatus of the foregoing type arise for several basicreasons. Since, for example, such operation requires that the partialpressure of the vapor be equal to the vapor pressure of liquid fromwhich it is derived at the temperature of the saturated mixture, itfollows that the fraction of the total gas flow which must be saturatedto produce a given concentration in the resulting total mixture mustvary with the temperature of the saturated mixture. Furthermore, it isfound in practice that the flow required to be delivered from thevaporizing apparatus varies over a reasonably broad range in accordancewith the requirements of a patient and of the particular application inwhich the apparatus is being utilized. While the simple scheme outlinedabove of dividing the total flow into substreams passing through andabout the vaporizing chamber may be effective for a relatively fixedrate of flow, apparatus in the past have not generally maintained suchconcentrations over a varying range of flow conditions.

Prior art vaporizing devices have attempted a solution of the problemsby maintaining a laminar flow of gas through the vaporizer so that theproportion of the two flow streams through the vaporizer remainconstant, despite changes in the total vaporizer flow. Such devices havebeen extremely difficult to manufacture, inasmuch as laminar flowrestrictors often introduce an excess of resistance into the flow path,or are very difficult to be produced, having predictable properties. Itis necessary, after manufacture, to individually calibrate suchVaporizers by actual test of flows through each vaporizer. Suchindividual calibration is expensive and is an undesirable manufacturingprocedure.

In accordance with the foregoing, it may be regarded as an object of thepresent invention to provide'vaporizing apparatus which ensures anoutput maintaining a fixed preset concentration level of vapor overwidely varying flow conditions, and over widely varying roomtemperatures, by the use of novel linear flow restrictors which insurelaminar flow throughout and yet provide extreme precision withoutintroducing any significant resistance to the flow paths.

SUMMARY OF THE INVENTION Now, in accordance with the present invention,the foregoing difficulties of prior art anesthetic Vaporizers have beenovercome and a vaporizer is described having a linear flow system whichinsures laminar flow throughout the vaporizer by including linear flowrestrictors having accurate predictability of flow therethrough.

In the vaporizer of the present invention, the total flow into thevaporizer is divided into two main gas streams. The first main gasstream passes through the linear flow restrictors and is then dividedinto two substreams by a concentration valve. By adjusting the con:centration valve, the ratio of the two substreams may be varied,however, the total flow remains unchanged. One of the substreams fromthe concentration valve is directed straight to the vaporizer outletwhile theother substream passes through the vaporizing chamber where itbecomes saturated by the liquid anesthetic before proceeding to andreuniting with the one substream at the vaporizer outlet.

The second main gas stream passes through a thermal compensation valveand thereafter is directed to the vaporizer outlet after being mixed,near the outlet, with the first gas stream. In the thermal compensationvalve, there are fixed linear flow restrictors through which one.substream of the second main gas stream passes and a series of on-offlinear flow restrictors where the other substream gas flow proceeds. Theon-off linear flow restrictors vary the flow of the other substream inaccordance with the sensed temperature in the anesthetic vaporizingchamber.

In each flow stream the linear flow restrictors are constructed in asimilar manner and comprise a plurality of parallel minute channelsformed coaxially in the peripheral surface of a cylindrical metalliccore. The outside area of the channels are confined by a ring which, inmanufacture, is heat shrunk around the core peripheral surface. An inletand outlet to each channel is provided to introduce and remove the gasflowing therethrough.

The formation of the linear flow restrictors thus is relatively easy toeffect, yet each channel, or series thereof, is extremely accurate andreproducible with existing manufacturing techniques.

Brief Description of the Drawings The invention is diagrammaticallyillustrated by way of example in the drawings appended hereto in which:

FIG. 1 is a schematic depiction in. cross-section of an anestheticvaporizer made in accordance with the present invention;

FIG. 2 is a longitudinal cross-sectional view of a preferred embodimentof a vaporizer made in accordance with the invention; the view is takenalong the line 2-2 in FIG. .3;

FIG. 3 is a transverse cross-sectional view taken along the line 3--3 ofFIG. 2;

FIG. 4 is a partial longitudinal cross-section taken along the line 44of FIG. 3;

FIG. 5 is an enlarged partial sectional view of a valve used in thepresent invention;

FIGS. 6 and 6A are respectively elevational and bottom plan views of theconcentration valve used with the invention; and

FIGS. 7 and 7A are respectively elevational and bottom plan views of thethermal compensation valve used with the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT In FIG. 1, there is shown asimplified schematic view of the anesthetic vaporizer in accordance withthis invention. Because the actual vaporizer construction is relativelycomplex, the overall operation will be first explained by reference toFIG. 1. The anesthetic vaporizer 10, shown schematically in FIG. 1,includes a gas inlet 12 and a gas outlet 14, each communicating,respectively, with inlet and outlet passageways l6 and 18. A furtherinlet passage 20'admits gas entering inlet 12 into an inlet chamber 22where the main gas flow is essentially divided into first and secondmain gas flows, which, for convenience, will be explained separately.

The first main gas flow enters a concentration valve, shown generally as24 in the direction depicted by arrow 26. The concentration valve 24 hasa slide member 28 in which is provided a linear flow restrictor 30through which all of the first main gas stream flows. The flowrestrictor 30'includes a plurality of minute, capillary-like flowpassages which produce laminar flow in the gas stream and insure alinear relationship between the flow and the pressure drop across theflow restrictor 30. The actual construction of flow restrictor 30 willbe later explained.

In the position shown in FIG. 1, the first main'gas stream flows throughlinear flow restrictor 30 and is divided into two substreams by divider32. One such substream enters vaporizing chamber 34 through vaporizingchamber inlet 36 where it becomes saturated with anesthetic 'vapor andproceeds through vaporizing chamber outlet 38 where it is channeled by arecess 40 in slide member 28 to outlet passageway 18 and through thevaporizer outlet 14. The other substream created by divider 32 proceedsthrough a'passage 42 into an outlet chamber 44 where it collects andmixes with further gas streams, as will be later explained, andeventually reunites with the saturated gas stream in outlet passageway18 via passage 46. Thus it may be seen that by changing the lateralposition of slide member 28 the relative proportions of the substreamscreated by divider 32 may be varied and since one substream becomessaturated by the anesthetic 48 in vaporizing chamber 34, theconcentration of anesthetic in the combined stream which eventuallyleaves the vaporizer outlet 14 may be controlled. As a further featureof the slide member 28, when it is in the far right position, not shown,the recess 40 serves to channel incoming gas in inlet passageway 16directly into outlet passageway 18 and the vaporizer chamber outlet 38is closed. Thus, the recess 40 serves as an on-off valve to shutaofi theflow'from the vaporizing chamber 34 while allowing a direct channel forgas entering inlet 12 to pass to outlet 14. The vaporizing chamber 34 isthen shut off, yet remaining open passages offer little flow resistanceand the vaporizer need not be physicallyremoved from the patientcircuit. It also can be seen that although the on-off type valve isshown integral with the concentration valve 24, it may be separatethere- Turning now to the second main stream from inlet chamber 22, thesecond main gas stream proceeds generally in the direction indicated bythe arrow 50 and is divided into two substreams by thermal compensatorvalve, shown generally at 52. One of such substreams passes through afixed linear flow restrictor 54 which is, as previously explained, aplurality of capillary-like passages. This substream then flows directlyinto the outlet chamber 44 and to the vaporizer outlet 14' by way ofpassage 46 and outlet passageway 18. The other substream enters avariable flow thermal bypass by entering linear restrictors 56 where theflow then passes a plurality of separate valves 58. Each valve 58 has avalve stem 60 of varying length and a common actuator 62. The valveactuator 62 moves the valves individually in accordance with theexpansion or contraction of a thermal motor, shown diagrammatically as abellows 64, acting in response to a sensor 66 located within thevaporizing chamber 34. As the temperature within vaporizing chamber 34goes up, the thermal motor, or bellows 64 expands and lifts more of theindividual valves 58 from their seats 68, thereby allowing more gas toflow through the variable thermal bypass to outlet chamber 44 and thusto the vaporizer outlet 14 via passage 46 and outlet passageway 18.

In the operation of the schematic, as shown, the incoming gas stream-isdivided into first and second main gas streams. The first main gasstream enters concentration valve 24 where it passes through linear flowrestrictor 30 and is divided into two substreams,one of which passesdirectly to the vaporizer outlet 14, and the other substream passesthrough vaporizing chamber 34 before being reunited with the onesubstream to the outlet 14. The concentration valve 24 can be adjustedto vary the concentration of the anesthetic in the combined flow streamleaving outlet 14. The second main gas stream flows through a thermalcompensator valve 52, where it is divided into substreams, one of whichpasses through fixed linear flow restrictors 54, and the other substreampasses through on-off flow restrictors where the flow is varied inaccordance with temperature changes in the vaporizing chamber. Sincethis second main stream eventually combines with the first main stream,its flow also determines the eventual anesthetic concentrationto thepatient. The fixed linear flow restrictors 54 are designed to allowsufficient gas flow therethrough for the lowest design temperature atwhich operation of the vaporizing chamber 34 can be expected. As thetemperature increases in vaporizing chamber 34, the substream from thefirst main gas stream picks up additional anesthetic since thesaturation pressure increases with the temperature of the anesthetic.The increased amount of anestheticpicked up is, therefore, compensatedby the movement of thermal motor 64 which senses the increase intemperature and expands to open a corresponding number of additionalvalves 58, increasing the total gas flow through the thermal compensatorvalve 52. Thus, changes in temperature of the anesthetic 48 arecompensated for and the final anesthetic concentration remains constant.Also, becauseall flows through the vaporizer are essentially laminar, bymeans of the linear flow restrictors, a change in overall flow does notaffect the relative pro portions of flow in any of the flow paths.

Referring nowto FIGS. 2 through 7 herein, an anesthetic vaporizer isshown which incorporates the various features set forth in thesimplified schematic apparatus of FIG. 1 in further detail. As thefollowing specification is read, it will be obvious that the descriptionof the preferred embodiment parallels the foregoing description of theschematic shown in FIG. 1.

In FIGS. 2-5, in particular, there is shown an anesthetic vaporizerhaving a manifold 70, FIG. 3, in which there is a gas inlet '72 and agas outlet 74. The gas entering inlet 72 proceeds through an inletpassageway 76 and, at bore 70, passes upwardly to inlet chamber 80 seenin FIGS. 2 and 4 which is formed beneath the top cover 02.

As the gas flow passes through inlet chamber 80, it is divided intofirst and second main gas streams which, for convenience, again will beexplained separately.

The first main gas flow enters a moveable concentration valve, showngenerally as M in FIG. 6 in the direction depicted by arrows 06, wherethe flow enters linear restrictors 00.

In FIGS. 6 and 6A, the construction of valve 84 containing the linearrestrictors 88 is shown comprising a cylindrical core 90 having aplurality of capillary-like passages 92 formed, coaxially, along theouter periphery of cylindrical core 90. A ring 94 surrounds the passages92 and seals them except for a minor part of the passages 92 extendingabove ring 94, shown at 96. In the preferred embodiment, a metal shim 98is wrapped about the periphery of core 90 and the passages themselvesare formed in the metal shim 98.

The ring 9d is heat shrunk around the metal shim 98,

' thereby sealing the passages 92 except for entrance openings 96. Theslots, once formed, receive a flow of gas and its passage therethroughbecomes laminar so that the relationship between pressure drop and flowthrough passages 92 is linear. The passages are extremely thin and longto achieve this linear relationship. When a metallic shim is used, theshim may be stainless steel stock having a thickness of 0.005 1 0.0001inch.

Application of the well-known Hagen-Poiseville laminar formula flowequation shows corresponding flow variations of i 5 percent. Byfabricating-all of the shims required for one vaporizer from one smallarea in a given sheet of metal stock, the thickness variations over thatarea will typically be less than i 0.0001 inch. In order to furtherminimize slot thickness variation due to machining burrs, the preferredmode of forming the slots is by etching techniques, ratherthanmechanical forming techniques.

In contrast with other means of achieving laminar flow, such as passageof gas through sintered metal, fine wire mesh and the like, the finalparameters of the present restrictors are predictable and do not varyextensively from one application to another, and the eventual vaporizerhas predictable properties.

At or near the bottom of passages 92, the flow of gas proceeds radiallyinwardly through tiny openings 100 where the flow then is directeddownwardly through drilled holes 102 and emerge at the bottom of thecore 90. As shown in FIG; 6A, each hole 102 emerges indi viduallycorresponding to each passage 92.

Returning to FIGS. 2 and 3, the flow path of the first main stream canbe seen entering the concentration valve 0d at arrows 86 where itproceeds downwardly through the capillary-like passages 92 of the linearflow restrictor 80, then entering radial openings 100 and leaves themovable valve 84 through drilled holes 102 where the first main flowstream is divided into two substreams by divider 103 in baseplate10d.The base plate 104 is a cylindrical body which is fixed in its positionin the vaporizer. As shown in FIG. 3 at the upper surface of baseplate104 there is formed two crescent shaped cavities 106 and 108, each ofwhich individually communicates with flow outlets and 112, FIG. 2. Theregion between crescen ts 106 and 108 comprises a divider 103. Thebottom of the valve 84 rests upon the upper surface of baseplate 104such that the drilled holes 102 communicate into the crescent shapedcavities 106 and 108. As the moveable core is rotated, the number ofdrilled holes 102 which communicate with each of cavities 106 and 108may be varied, thus the relative proportion of flow through divideroutlets 110 and 112 can be selectively varied by rotating moveable valve84.

Inthis manner, the first main flow stream is selectively divided intoone substream passing through divider outlet 110 downwardly throughvaporizing chamformed in the exterior of flow guide 122 where it spiralsdownwardly in close association with outer tubular fabric wick 124,saturated with liquid anesthetic contained within outer casing 126.

The anesthetic level itself is not shown, nor are conventional drainsforremoving anesthetic or a filler for introducing anesthetic into thevaporizing chamber 116 as both are conventional in the art. At the lowerend of outer spiral passage 120, the substream enters crossover passage128 and then proceeds upwardly through inner spiral passage 130 in closeassociation with anesthetic-saturated inner wick 132 where it againpasses through a cross-over bore 134 to an upper spiral 136 andeventually flows from vaporizing chamber 116 through vaporizing chamberoutlet 138 in FIG. 4. The now saturated substream flows through anon-off valve, is mixed with the other gas stream and proceeds to thevaporizer outlet 74 as will be later explained.

Thus, it may be seen that by rotating the moveable concentration valve84, the proportions of the first main stream flowing through thevaporizing chamber 116 and bypassing the same can be selectively varied.

The cylindrical core 90 is biased downwardly to effect a seal againstthe upper surface of baseplate 1041, as shown in FIGS. 2 and 4, by alower springguide 140 which bears against an inner ledge on core 90. Acompression spring 152 is positioned between lower spring guide 140 andupper spring guide 154 both spring guides being centered in position byvalve guide 156. The upper spring guide 154 is held in positioncompressing spring 152 by a drive pin 158, the ends of which, FIG. 2,Le, rest in slots in the upper edge of cylindrical core 90 and thecenter of which is positioned in a slot through the lower end of valvestem 160, supported against top cover 82. Concentration control knob 162is affixed to valve stem and, as will be seen, by rotating control knob162, the moveable conchange the desired concentration of the anestheticvapor from the vaporizer outlet.

As a further feature of the anesthetic concentration valve 84, an on-offvalve 164 is provided which is also operable by rotation of control knob162. This valve is shown particularly in FIGS. 4 and 5 and, in the solidposition shown, the valve plug 166 is seated against the vaporizingchamber outlet 1138, thereby preventing any anesthetic saturated gaspassing from the vaporizing chamber 116 to the vaporizer outlet '74 viapassage 168 and outlet passageway 170, see FIG. 3. In this position,therefore, gas may enter the vaporizer inlet 72, pass directly through across bore 172 of FIG. 5 which joins inlet passageway 76 and outletpassage 168 so that the gas can directly pass from the vaporizer inlet72 to the outlet 71 with a minimum of flow resistance. In this positionof valve plug 166, there are no drilled holes 102 in cylindrical core 90which align with the crescent shaped cavity 106 so that there is also nogas flow into the vaporizing chamber.

As the control knob 162 is rotated, the valve stem 174 of on-off valve164 is raised by result of a spring bias in the upward direction imposedby spring 176, seated at its lower end and acting against earn follower178 at its upper end. A cam 180 within control knob 162 further recedesinto the knob 162 and, as the knob 162 is rotated, cam follower 178follows the receding cam 180 upwardly, thereby allowing valve plug 166to lift fromvaporizing chamber outlet 138 to eventually seat at upperseat 182 to prevent gas from flowing from cross bore 172 to the outletpassage 168. Thus, all of the gas entering the vaporizer proceeds intothe inlet chamber 00 and none is bypassed directly to the outlet 74. Atthis point of rotation, the position of the linear passages 92 inconcentration valve 84 is such that further rotation causes some, thenan increasing number of the drilled holes 102, to communicate withcrescent shaped cavity 106 to introduce gas into the vaporizing chambear116. Further rotation of the control knob 162 increases the proportionof gas through vaporizing chamber 1116, yet the overall total gas flowof the first gas stream remains constant, i.e., as the substream gasthrough vaporizing chamber 116 is increased, there is a correspondingdecrease in gas flow of the substream bypassing the vaporizing chamber116.

Turning now to the second main gas stream from inlet chamber 00, FIGS. 2and 4, the second gas stream proceeds generally in the directionindicated by the arrows 103 into a linear flow restrictor 184 of thermalcompensator valve shown generally at 1105. Again, the linear flowrestrictor 1 is formed by a plurality of capillary-like passages res inthe same manner as linear flow restrictor 08., and, as shown in FIGS. 7and 7A, the passages 106 are located around the external periphery ofcylindrical core 188. Again, the passages 186 are preferably formed inthin metallic shim 1190, held about the perimeter of core 188 by a ring1192, heat shrunk into position while leaving an inlet opening 194 atthe top of the passages 11%. As the second main stream passes throughthe restrictor passages 186, it is divided into two substreams, one ofwhich proceeds radially inwardly through outlet openings 196, downwardlythrough drilled holes 198 and into the outlet chamber 110, see FIG. 2.The other substream proceeds through on-off thermal bypass valves viaradial openings 200, FIG. 2, and into individual chambers 2041, eachhaving a valve 205 shown in the shape of a r ball, separating eachchamber 204 from the outlet chamber 118. Each valve ball 205 is actuatedby a valve stem 206 of varying length fixed to a common actuator 208.The valve actuator 208 moves the valves 205 individually in accordancewith the expansion or contraction of a thermal motor 210 located withinvaporizing chamber 116. The thermal motor 210 is of generallyconventional construction and may consist of expanding bellows whichmoves valve actuator 208 upwardly or downwardly in accordance with thesensed temperature of the anesthetic within vaporizing chamber 1116. Asshown in FIG. 2, the thermal motor 210 includes a stem 212 which movesup or down depending upon, respectively, an increase or decrease oftemperature in vaporizing chamber 116.

A combination of springs-213 and 214 retains the stem 212 activelyengaging the valve actuator throughout its total stroke, as shown. Sincethe many valve stems 206 are of differing lengths, the relative positionof the valve actuator determines, at any time, how many of the valves205 are open and how many are closed. As the temperature withinvaporizing chamber 116 increases, the valve actuator moves upwardly andopens more valves 205 so that additional flow proceeds through thethermal compensator valve 185 to outlet chamber 118. Thus, the total ofthe second main stream is temperature compensated, as the temperature ofanesthetic increases, additional flow passes through the thermalcompensator valve 185 to off-set the increased pickup of anesthetic fromthe vaporizing chamber 116 by the first main gas stream. By this means,the thermal compensator valve includes a fixed linear flow restrictor184 through which the second main stream passes and then creates twosubstreams, one of which passes through a series of onoff valves whichvary flow in accordance with the temperature of the anesthetic vapor.The fixed restrictors are designed to allow sufficient flow through toachieve the desired outlet anesthetic concentration for the lowestdesign temperature at which the anesthetic will be used. As thistemperature increases, therefore, additional flow is automaticallyallowed through the series of on-off valves. Again, all of the secondmain gas stream passes through the specially designed linear flowrestrictors.

The outlet chamber 118 thereby receives all of the flow from the secondmain gas stream as well as that proportion of gas flow of the first maingas stream that does not pass through the vaporizing chamber. The flowfrom outlet chamber 118 proceeds upwardly through outlet bore 216, seeFIG. 3, through passage 218 and reunites in outlet passageway 1'70 withthe anesthetic-saturated flow of gas from the vaporizing chamber 116,thus the combined flow of gas passes through the vaporizer outlet 74.

While the present invention has been particularly described in terms 'ofa specific embodiment thereof, it will be understood, in view of thepresent disclosure, that numerous variations may be made withoutdeparting from the teachings of the overall invention. Accordingly, theinvention is to be broadly-construed and limited only by the scope andspirit of the claims now appended hereto.

. I claim:

1. An anesthetic vaporizer apparatus, comprising in combination:

a vaporizer housing having a main gas inlet and a main gas-vapor outlet,

a bypass passageway communicating between said gas inlet and said gasoutlet,

a vaporizing chamber in said housing for containing liquid anestheticand adapted to saturate gas passing through said vaporizing chamber withanesthetic vapor,

vaporizing passage means adapted to direct a portion of gas from saidmain inlet through said vaporizing chamber to said outlet,

thermal bypass passageway communicating between said gas inlet and saidgas outlet and adapted to control the flow of gas through said thermalbypass passageway in accordance with the temperature within saidvaporizing chamber,

linear flow restrictors in each of said vaporizing passage means andthermal bypass passageway,

said linear flow restrictors comprising a plurality of minute capillarypassages adapted to maintain a linear relationship between the gas flowand pres.- sure drop across said flow restrictors.

2. An anesthetic vaporizing apparatus as defined in claim 1 whereiinsaid capillary passages further comprise inner and outer annular rings,an annular thin metallic ring of stock being compressed between I saidinner and outer rings, said metallic ring having'narrow, parallelaxially disposed slots, and inlet and outlet means for providing gasflow into one end and from the other end of said slots for providing acontinual flow path through said slots.

3. An anesthetic vaporizer apparatus, comprising in combination:

a vaporizer housing having a main gas inlet and a main gas-vapor outlet,

a bypass passageway communicating between said gas inlet and said gasoutlet,

a vaporizing chamber in said housing for containing liquid anestheticand adapted to saturate gas passing through said vaporizing chamber withanesthetic vapor,

vaporizing passage means adapted to direct a portion of gas from saidmain inlet through said vaporizing chamber to said outlet,

thermal bypass passageway communicating between said gas inlet and saidgas outlet and adapted to control the flow of gas through said thermalbypass passageway in accordance with the temperature within saidvaporizing chamber,

linear flow restrictors in each of said bypass passageway, vaporizingpassage means and thermal bypass passageway,

saidlinear flow restrictors comprising a plurality of minute capillarypassages adapted to maintain a linear relationship between the gas flowand pressure drop across said flow restrictors.

4. An anesthetic vaporizing apparatus as defined in claim 3 wherein saidcapillary passages further comprise inner and outer annular rings, anannular thin metallic ring of stock being compressed between said innerand outer rings, said metallic ring having narrow, parallel axiallydisposed slots, and inlet and outlet means for providing gas flow intoone end and from the other end of said slots for providing a continuaiflow path through said slots.

5. An anesthetic vaporizer apparatus as defined in claim 3 furtherincluding a concentration valve means adapted to selectively vary theproportion of main gas directed through said bypass passageway and saidvaporizing passage means.

6. An anesthetic vaporizing apparatus as defined in claim 3 wherein saidthermal bypass passageway comprises a plurality of individual passages,each having a valve, each said valve means being individually operatedto open or close in accordance with the temperature within saidvaporizer chamber.

7. An anesthetic vaporizing apparatus as defined in claim 6 includingtemperature detecting means in said vaporizing chamber and actuating;means connected to said detecting means for individually operating saidvalves in accordance with the temperature detected within saidvaporizing chamber.

8. An anesthetic vaporizing apparatus as defined in claim 7 wherein eachsaid valve comprises a ball normaily closing each such individualpassage and said actuating means comprises a plurality of valve stems ofdiffering length, each of which is adapted to be raised to lift acorresponding individual ball to open each such individual passage, anda common operating member adapted to move said plurality of valve stemsa predetermined distance in response to a change in temperature withinsaid vaporizing chamber.

1. An anesthetic vaporizer apparatus, comprising in combination: avaporizer housing having a main gas inlet and a main gas-vapor outlet, abypass passageway communicating between said gas inlet and said gasoutlet, a vaporizing chamber in said housing for containing liquidanesthetic and adapted to saturate gas passing through said vaporizingchamber with anesthetic vapor, vaporizing passage means adapted todirect a portion of gas from said main inlet through said vaporizingchamber to said outlet, thermal bypass passageway communicating betweensaid gas inlet and said gas outlet and adapted to control the flow ofgas through said thermal bypass passageway in accordance with thetemperature within said vaporizing chamber, linear flow restrictors ineach of said vaporizing passage means and thermal bypass passageway,said linear flow restrictors comprising a plurality of minute capillarypassages adapted to maintain a linear relationship between the gas flowand pressure drop across said flow restrictors.
 2. An anestheticvaporizing apparatus as defined in claim 1 whereiin said capillarypassages further comprise inner and outer annular rings, an annular thinmetallic ring of stock being compressed between said inner and outerrings, said metallic ring having narrow, parallel axially disposedslots, and inlet and outlet means for providing gas flow into one endand from the other end of said slots for providing a continual flow paththrough said slots.
 3. An anesthetic vaporizer apparatus, comprising incombination: a vaporizer housing having a main gas inlet and a maingas-vapor outlet, a bypass passageway communicating between said gasinlet and said gas outlet, a vaporizing chamber in said housing forcontaining liquid anesthetic and adapted to saturate gas passing throughsaid vaporizing chamber with anesthetic vapor, vaporizing passage meansadapted to direct a portion of gas from said main inlet through saidvaporizing chamber to said outlet, thermal bypass passagewaycommunicating between said gas inlet and said gas outlet and adapted tocontrol the flow of gas through said thermal bypass passageway inaccordance with the temperature within said vaporizing chamber, linearflow restrictors in each of said bypass passageway, vaporizing passagemeans and thermal bypass passageway, said linear flow restrictorscomprising a plurality of minute capillary passages adapted to maintaina linear relationship between the gas flow and pressure drop across saidflow restrictors.
 4. An anesthetic vaporizing apparatus as defined inclaim 3 wherein said capillary passages further comprise inner and outerannular rings, an annular thin metallic ring of stock being compressedbetween said inner and outer rings, said metallic ring having narrow,parallel axially disposed slots, and inlet and outlEt means forproviding gas flow into one end and from the other end of said slots forproviding a continual flow path through said slots.
 5. An anestheticvaporizer apparatus as defined in claim 3 further including aconcentration valve means adapted to selectively vary the proportion ofmain gas directed through said bypass passageway and said vaporizingpassage means.
 6. An anesthetic vaporizing apparatus as defined in claim3 wherein said thermal bypass passageway comprises a plurality ofindividual passages, each having a valve, each said valve means beingindividually operated to open or close in accordance with thetemperature within said vaporizer chamber.
 7. An anesthetic vaporizingapparatus as defined in claim 6 including temperature detecting means insaid vaporizing chamber and actuating means connected to said detectingmeans for individually operating said valves in accordance with thetemperature detected within said vaporizing chamber.
 8. An anestheticvaporizing apparatus as defined in claim 7 wherein each said valvecomprises a ball normally closing each such individual passage and saidactuating means comprises a plurality of valve stems of differinglength, each of which is adapted to be raised to lift a correspondingindividual ball to open each such individual passage, and a commonoperating member adapted to move said plurality of valve stems apredetermined distance in response to a change in temperature withinsaid vaporizing chamber.